1. Field of the Invention
The present invention relates to the field of aeronautical equipment. It relates more specifically to heat dissipation systems, and even more particularly heat sinks for turbomachine-type aircraft propulsion units.
2. Description of the Related Art
A large number of aircraft propulsion units comprise a turbomachine; this is the case, for example, for propfan-type aircraft propulsion units, where this turbomachine drives two counter-rotating rotors.
In these propulsion units, a gearbox (gears between the turbomachine axle and the rotors) transmits the mechanical energy generated by the turbomachine to the rotors.
Although it has very high efficiency, this gearbox dissipates part of the energy created by the propulsion unit into heat by friction. This heat is transmitted in particular to the gearbox lubricant.
Moreover, the turbomachine itself generates significant heat dissipation mainly by mechanical friction, also through its lubricant.
It is clear that this heat must be dissipated to the outside environment to cool the propfan.
Various solutions have been developed to perform this cooling.
A first solution, close to the state of the art of turbofans (see for example patent application FR2006/0052654), consists of collecting air over a compressor stage (low pressure so that temperatures are not too high), positioning an air/oil exchanger in this air flow, positioning an air regulator valve, and having the air exit tangentially to the outer surface of the nacelle to recover a portion of the thrust. On thermal design points (ground on a hot day, for example), the valve is completely open and, despite the fact that the airplane is immobile, the air exchanger is supplied. In flight, to limit the impact on performance, the air valve is partially open in order to adjust the air flow. The major drawbacks of this solution are:                Significant impact on the engine's performance due to the collection of air (the turbomachine must be sized taking this loss of flow into account)        Acoustic impact of ejecting air upstream of the propellers and on a discrete position (non-annular)        Distortion of the nacelle's external aerodynamic flow, which can lead to a reduction in the propellers' efficiency.        